1. Field of the Invention
The present invention relates to a storage battery, and more particularly to a structure of a battery casing having a thinner, see-through window portion for visual recognition of a level of electrolyte from the outside.
2. Description of the Background Art
Electrolyte is contained in a battery casing of a storage battery. Conventionally, there existed a storage battery having a thin-walled see-through window portion provided at a battery casing for visual recognition of a level of electrolyte from the outside. In FIG. 6, an exemplary storage battery with a conventional see-through window portion is shown.
As shown in FIG. 6, a storage battery 1 has a battery casing 3, a cover 2, and a thin-walled see-through window portion 4 on a sidewall of battery casing 3. Because of such a see-through window portion 4, a level of electrolyte contained in battery casing 3 is visually recognizable from the outside and the amount of the electrolyte can be externally grasped.
When the thin-walled see-through window portion 4 is provided on the sidewall of battery casing 3 as described above, however, material flow is hindered in this part when battery casing 3 is molded, thereby deteriorating the moldability of battery casing 3.
Furthermore, see-through window portion 4 is thin and thus weak in strength, so that see-through window portion 4 easily deforms when battery casing 3 is released from a mold.